Opiates have been the subject of intense research since the isolation of morphine in 1805, and thousands of compounds having opiate or opiate-like activity have been identified. Many opioid receptor-interactive compounds including those used for producing analgesia (e.g., morphine) and those used for treating drug addiction (e.g., naltrexone and cyclazocine) in humans have limited utility due to poor oral bioavailability and a very rapid clearance rate from the body. This has been shown in many instances to be due to the presence of the 8-hydroxyl group (OH) of 2,6-methano-3-benzazocines, also known as benzomorphans [(e.g., cyclazocine and EKC (ethylketocyclazocine)] and the corresponding 3-OH group in morphinanes (e.g., morphine).

The high polarity of these hydroxyl groups retards oral absorption of the parent molecules. Furthermore, the 8-(or 3-)OH group is prone to sulfonation and glucuronidation (Phase II metabolism), both of which facilitate rapid excretion of the active compounds, leading to disadvantageously short half-lives for the active compounds. Until the publications of Wentland in 2001, the uniform experience in the art of the past seventy years had been that removal or replacement of the 8-(or 3-)OH group had led to pharmacologically inactive compounds.
U.S. Pat. No. 6,784,187 (to Wentland) disclosed that the phenolic OH of opioids could be replaced by CONH2. In the cyclazocine series of opioids, it was shown that 8-carboxamidocyclazocine (8-CAC) had high affinity for μ and κ opioid receptors. In studies in vivo, 8-CAC showed high antinociception activity and a much longer duration of action than cyclazocine (15 h vs. 2 h) when both were dosed at 1 mg/kg ip in mice.
Quaternary derivatives of the opioid antagonist naltrexone have been disclosed for preventing or relieving the intestinal mobility inhibiting side effects of narcotic analgesics such as morphine and related opiates without impairing the analgesic activity of the narcotic analgesic. Methylnaltrexone, for example, was disclosed in U.S. Pat. No. 4,176,186 (to Goldberg et al.). However, the dose required to prevent or inhibit intestinal motility inhibiting side effects is relatively high. Thus, a need exists to develop compounds with increased activity at lower doses.